QuestionQUESTION: hi howard, thanx for advice on my electrics in the summer , all sorted now, major restoration of my 68 tourer now complete and on road 4 first time in 22 years. i do have one problem though;
when flicking ignition switch fuel pump clicks to prime carbs , when engine is fired up fuel pump continues to click at fast rate and does not slow down at all even when engine is running it continues to pump at same fast rate.i thought fuel lines might have an air leak so i retightened all unions and joints ,to no avail.pump doesnt slow down at all(shouldnt it pump fuel fast at first and slow down to a slow click when carbs are full?)its a brand new pump, i couldnt have wired it wrong could i? could problem be at carb end? also car runs fine at low speed but once i accellerate car has no power and backfires when changing from 2nd to 3rd on verge of cutting out many thanx, simon ,ENGLAND
ANSWER: Hi Simon,
If it is an SU pump and it is built correctly it will click fast until the carbs are full, then it should slow down on the rate of clicks when idling and maybe pick up just a little when driving but it should not run fast all the time.
If the carbs are not flooding or there is no fuel leaking anywhere and it is still running fast, you need to put a "T" in the fuel line close to the carburetors and run a long hose out from under the hood (bonnet) and put a fuel gauge under a wiper arm so you can read the pressure under acceleration and at speed. The pressure should maintain 1.5 to 3 PSI at all times. If it is lower than that and you are sure it is not leaking fuel nor flooding then I would suspect the fuel pump has either a leaking valve or the manufacture didn't adjust the diaphragm pin correctly. You could also run another test by disconnecting the fuel line from the carbs and connect the line just to the gauge and bleed all of the air out of the line by loosening the connection to the gauge then tighten it up with the pump turned on. If the pump does not stop clicking then the pump is either defective or you have a air leak in the tank pick up. A sure test of the pump would be then to connect a line to the pump and put the intake line into a can of fuel and the outlet (after bleeding all of the air out) to the gauge only. If the pump continues to run it is for sure bad. The electric solenoid retracts the diaphragm and the spring is what pushes the fuel. When the fuel is stopped and there is no air in the line the diaphragm does not move because you can not compress a liquid. However if the inlet valve in the pump is leaking the fuel will bleed back into the tank thus allowing the diaphragm to move and click over the contact points again and again.
Howard
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QUESTION: thanks howard for super fast response.with regards to carbs they were acquired second hand but were said to be refurbished ready to run, how would i know if they were flooding?.would i be better to have them set up properly first before tackling the pump problem(could this be done while the pump runs continually?).if carbs prove not to be flooding,i dont quite understand how one would connect a fuel line to a fuel gauge, all my gauge has at the back of it are 2 electrical terminals no facillity for attatching a fuel line,(i'm probably being a little naive on that one )and my fuel gauge only reads empty or full ,not pressure .is there anything else i could use to measure the pressure ? an old but working oil gauge perhaps?.all the best simon
AnswerIf it were flooding it would be running very rough at low RPM and blowing a lot of black smoke out the tail pipe.
As for the gauge, you need to purchase a hydraulic fuel pressure gauge at most any auto parts store. (they are not expensive and some vacuum gauges have a fuel pressure section on them thus two test gauges in one) You will probably need to buy a "T" fitting and some extra hose at the same store and don't forget to use hose clamps as you don't want a fuel hose to come off while testing.
Howard
